This. Don't be the one to escalate things, and don't feel like you need to defend your SO unless they can't defend themselves.

If you're situation is an ongoing thing, that seems to be something that could escalate (repeated public harassment), I'd recommend one that you're good at that you can learn relatively quickly or something that gives quick results. I'm sure people could give better advice on what might do that than I could. Also let the police know depending on how bad this guy (or guys) gets if this continues.

Also as an aside, I want to say damn you Kickpuncher for taking my first choice for a name, and ask why you don't have Abed or Annie in a gi as your avatar.